A yarn winder is used for winding of continuously arriving yarn of polyolefin—flat/fibrillated or any similar type—onto a bobbin. Here, yarn defines flat tapes, multifilament and monofilament yarns or any similar type of yarns or tapes. In general, bobbin holders, also known as mandrel cores, are mounted on spindles on each winder machine frame. Each spindle needs precisely controlled rotation, so may be driven independently by an electric motor through a suitable mechanism such as a belt and pulley arrangement or with a direct driving system. Conventionally, the encoders or other similar devices for pulse generation are mounted on the motor for monitoring the motor revolutions, and the signal therefrom is communicated to the electronic controller with the help of suitable cable. The controller further sends the electrical signals to the inverter/drive of the active motor which determines the power to be given for the motor driving the spindle.
The conventional winders of the above type are disclosed in the U.S. Pat. Nos. 5,228,630, 4,765,552 and European Patent 861800A2.
In these conventional winders, yarn winding tension is controlled by regulating tightening of the oscillating arm tensioning spring (hereinafter referred to as a, dancing arm resistance for onwards references). The to and fro motion of dancing arm is monitored electronically to keep yarn delivery at nearly uniform tension with constant linear speed to spindle.
Wound bobbins produced from winders are used for further in line applications as necessary. One of the major applications of wound bobbins is in formation of tubular sacks on Circular Weaving Machines, which are also known as Circular Weaving Looms (CWM/CWL). Circular looms contain plurality of bobbins of slit film tapes used as weft and warp. Weft bobbins are arranged around a circular reed ring, such that as the main shaft drives the central part, weft bobbins start moving along the reed ring path and woven fabric produced is taken off by the fabric take off unit.
In conventional winders, winding tension of yarn is maintained by providing resistance to the motion of the dancing arm by adjusting spring attached to it. Position feedback of dancing arm is routed to the control logic of winders, which in turn rotate the bobbin mandrel such that a position of dancing arm is maintained consistently with least oscillation. To maintain the winding tension for various types of yarn of different properties like denier, width etc., the spring attached to the dancing arm is adjusted such that its variation is minimized as much possible to achieve good quality of produced bobbins. Conventionally, spring associated with dancing arm is set once at the start of the winding process, which remains constant throughout build of the bobbin as product. When the yarn from the bobbins is used as the weft yarn on a circular loom, its unwinding tension increases as the size of the bobbin decreases. This might be due to high pulling force required for rotating the bobbin at increased angular velocity, or any other unidentified reasons during winding. This increase in yarn unwinding tension results in undesirable variation in the fabric width—particularly so as weft bobbin size reduces with time. This, however, also increases necking of the fabric produced and sometimes breakage due to high weft tension.
To produce a good quality fabric of uniform width (or fabric without unacceptable variation in width), it is necessary to vary the tension in the weft bobbin tape, especially below a certain bobbin size. This variation in tension is carried out gradually or discretely from a lower to higher level as the bobbin size grows.
DE2100566A1 discloses an apparatus for regulating winding tension as a function of the bobbin diameter in a slit-film or yarn winder and discloses that the tension setting device for changing the yarn tension used therein changes the tension as a function of the bobbin diameter.
DE1129096B state that “in order to obtain a good winding structure, it has also already been proposed to vary this loading or unloading of the thread feeler as a function of the growing roll or of the emigration or position of the feeler lever so that the thread tension decreases during the winding setup.” It further provides a means for doing so.
DE3913794 state that “for certain winding-up purposes, it is also advantageous to reduce the yarn tension acting with increasing winding diameter in order to avoid bulging on the winding. In this, therefore, a device is required for adjusting the thread tension in the overall course of the winding of a thread winding.” It further provides a means for doing so.
However, these documents do not teach how to change the winding tension as a function of the bobbin diameter in discreet pressure change by means of selecting a specific pressure line.
There is therefore a need to develop a method of changing yarn winding tension such that when same bobbin is unwound, the weft tension is lower compared to conventionally wound bobbin at same bobbin size, to generate uniform quality woven fabric.